New Topic Do some revision for tomorrow’s exam whilst you are waiting

Last lesson Measuring the energy content of two fuels You will move to the next experiment at the appropriate signal.

Energy Content of two fuels FuelInitial mass (g) Final mass (g) Mass of fuel used (g) Initial temp of water (°C) Final temp of water (°C) Temp rise of water (°C) Energy released (J) Energy released per gram of fuel (J/g) Wax Ethanol Volume of water (cm 3 ) x 4.2 x temp rise Energy ÷ mass Then write three sentences saying what you have discovered, and suggesting two ways the experiment could be improved.

Today’s lesson Sankey diagrams Efficiency What is electricity?

Wasted Energy

Can you read carefully (in silence) pages 132 and 133 of your book?

Energy transfer (change) A lamp turns electrical energy into heat and light energy

Sankey Diagram A Sankey diagram helps to show how much light and heat energy is produced

Sankey Diagram The thickness of each arrow is drawn to scale to show the amount of energy

Sankey Diagram Notice that the total amount of energy before is equal to the total amount of energy after (conservation of energy)

Efficiency Although the total energy out is the same, not all of it is useful.

Efficiency Efficiency is defined as Efficiency (%) = useful energy outputx 100 total energy input

Example Efficiency = 75 x 100 = 15% 500

Energy efficient light bulb Efficiency = 75 x 100 = 75% 100

Energy efficient light bulb Efficiency = 75 x 100 = 75% 100 That’s much better!

More complex examples

Let’s try the questions on pages 132 and 133

What is electricity?

Stand up! ☺

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☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ cell energy electron lamp

☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ cell energy electron lamp Can you copy this please?